1. Field of the Invention
This invention relates to a method of bonding loudspeaker diaphragms, and more particularly to a method of bonding loudspeaker diaphragms formed of an olefinic resin.
2. Description of the Related Art
Generally, a rubber, acrylic or epoxy adhesive is used in bonding a surround, a voice coil bobbin and a dust cap to a loudspeaker diaphragm formed of an olefinic resin such as polyethylene or polypropylene, or a polyester resin.
An olefinic resin is a crystalline resin having little or no polarity, which makes bonding difficult. To improve the adhesive property, a method has been proposed which applies a surface treatment to bonding positions such as surface polishing, flame treatment, chemical treatment, corona discharge, plasma treatment, or ultraviolet radiation. In another method, a helical groove making at least one circle is formed in each bonding position to produce a screw-like effect, thereby securing a necessary bonding strength (Japanese Patent Publication Kokai No. 1988-283395). In a further method, a silicone rubber adhesive is used as an adhesive or an adhesion primer (Japanese Patent Publication Kokai No. 1984-86399).
These treatment methods have the following disadvantages. A surface treatment is carried out to form polar groups such as --OH group, --COOH group and --NH.sub.2 group on a nonpolar surface of an olefinic resin. Surface polishing has the disadvantage of injuring the surface and impairing the appearance of products. A flame treatment is not entirely satisfactory with regard to uniform surface finish, and could be dangerous to operators. A chemical treatment poses a problem of pollution, and subjects operators to danger. A corona discharge loses its effect several hours from the execution. A plasma treatment and ultraviolet radiation require sophisticated and costly equipment, and may endanger operators. The method of forming helical grooves extending through at least one circle results in a complicated manufacturing process, low productivity and high cost. The method in which a silicone rubber adhesive is used as an adhesive or an adhesion primer fails to assure a sufficient bonding strength, whereby the components could be separated by sudden, great vibrations.
With digitalization of sound sources and increased outputs of amplifiers, there is a mounting demand today for high input durability loudspeakers based on an increased bonding strength. However, none of the conventional methods of bonding loudspeaker diaphragms formed of an olefinic resin are satisfactory, or effective without relying on large and expensive equipment.